Getting ready for climate change by creating riparian shade Purpose: This guidance has been produced to support the creation of shade over rivers using riparian trees and vegetation (riparian shade). The focus is on maintaining suitable freshwater habitat for salmon and brown trout (salmonid) populations that we expect to be at risk from the effects of climate change. It has been written to explain the benefits of riparian shade (sections 1 and 2) and provide consistent advice on creating riparian shade (sections 3-10) to support the Environment Agency‟s initiative on Keeping Rivers Cool. It has been designed for use by the Environment Agency „Keeping Rivers Cool‟ pilot catchment officers and „Keeping Rivers Cool‟ leads in external partner organisations. As we gather more information on best practice ways of creating riparian shade we will add to and develop this guide, making it more widely available to land owners and other interested organisations in the second year of the project.

How to use this guide: This is designed to be used as a digital guide containing brief summarised information on creating riparian shade. It contains embedded electronic links to additional useful information. Because of these electronic links it is easier to use the guidance on a computer (rather than a print out) in order to go straight to recommended websites.

If you would like to suggest any changes to this document, let someone know that an electronic link needs updating, or have further information that could be included, please contact Rachel Lenane.

1.1 Climate change and river temperature Predicting the future is fraught with uncertainty however, climate experts have tried to capture some of this uncertainty in the current set of scenarios for the UK in the UKCP09 projections1. The models predict that average summer air temperatures will warm by between 2°C and 4°C by the 2050s compared to the longterm 1961-90 average temperature. River temperatures are sensitive to changes in climate and water temperatures are expected to rise by a similar amount2. It may not seem much but even small changes like this can have an impact on the health of wildlife living in freshwaters. Brown trout and salmon are particularly vulnerable to predicted climate change. A rise in water temperature above 22°C for more than seven consecutive days can be lethal for brown trout3.

The Environment Agency is looking at ways of keeping rivers cool and taking action now to prevent, where possible, rivers in England and Wales becoming inhospitable for our freshwater wildlife over the next 60-70 years. Trout and salmon populations in England and Wales are already under stress with some rivers reaching temperatures above the lethal limit for these species during recent hot, dry summers.

Historically natural rivers, streams and their floodplains across the UK were more densely wooded, and woody debris would have been a common feature in river channels4. Much of this tree cover has been lost and many rivers now lack shade. Riparian trees and shrubs can help reduce local stream temperatures on hot summer days. Summer mean and maximum water temperatures are on average 2-3ºC lower in shaded than in open rivers5. Increasing tree and shrub cover in the riparian zone will also help to provide a natural source of in stream woody debris. Woody debris is beneficial for many species of plants, invertebrates and fish6. Leaf litter accumulates against woody debris and is an important food reserve for shredding macroinvertebrates. Research in the UK showed 147 invertebrates, some rare, were strongly associated with woody debris7. Otters also use woody debris for “resting” sites. It also has a key role in protecting salmonid fish through the creation of thermal refugia as water temperature at the stream bed can be significantly cooler than at the stream surface particularly during periods of low flow when temperatures are likely to be highest. EA staff should see our internal policy position, „Woody debris in rivers (43_12)8‟, for more information on this topic.

In the right location natural regeneration, through livestock exclusion and fencing-off lengths of river, is a good habitat restoration method as the new woodland will closely match existing woodland in proximity to the site. Natural regeneration also has a good survival rate, so if the site and time frame allows it is also a cost effective method of woodland creation. Where planting is more appropriate (or a combination of natural regeneration and planting) a planting design plan should be prepared which takes account of specific site conditions, appropriate sources for plant stock and includes consideration of future management.

In certain circumstances other interventions for cooling rivers for example, river restoration, heated effluent control, modified abstraction regimes and water meadow management may also be beneficial and we will be exploring these in the future. In the mean time we aim to help create riparian shade where we think it will have the greatest benefits for river ecology.

Jenkins, G.J., Perry, M.C., and Prior, M.J. (2008) Webb, B.W. & Nobilis, F. (1997) 3 Elliott, J. M. & Elliott and J. A. (2010) Peterken, G.F., Hughes, F.M.R. (1995) Bowler, D.E., et al.(2012) & Caissie, D. (2006) Braccia, A. & Batzer, D.P. (1999) Godfrey, A. (2003) Environment Agency (2012) Although there are still some knowledge gaps about the cooling effects of introducing more riparian trees we can‟t ignore the risks of climate change to river conservation. Creating riparian shade in the right places can also provide a range of wider ecological benefits. We recognise that it is not a standalone measure to managing warming in rivers, but it is a low-risk reversible action, providing a range of ecosystem services and a good start to keeping rivers cool.

1.2 Optimum river temperatures for salmon and brown trout

Water temperature affects all physical, chemical and biological processes in the freshwater environment and it displays natural diurnal and seasonal variations, dependent on location and climate9. These daily temperature fluctuations are more pronounced in small streams, particularly if they are not shaded by riparian vegetation.

In freshwater systems most species have a specific temperature range in which they can live. Salmonids require temperatures of between 5 and 15°C for normal growth and temperatures above 22°C for more than seven consecutive days can be lethal for brown trout 10. In smaller fresh water streams in Southern England, temperatures in excess of 31°C have already been recorded11. These recorded temperatures highlight the need to take action to try and reduce water temperatures in streams in order to protect trout and salmon populations and maintain a suitable habitat to support them.

1.3 Wider ecological benefits of riparian vegetation

The influence riparian trees have on the habitat quality of the river is determined by tree species, extent and structure of the woodland, and the topography of the riparian zone. Organic inputs from the riparian zone in the form of leaf litter, and insects can account for up to 50% of the energy in a river system. The many benefits provided by riparian vegetation ( Figure 1) in helping to maintain natural stream functions are shown in Table 1.

Table 1. The functional roles of different vegetation components of the riparian zone and adjacent land (provided by SKM Enviros).

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Figure 1. The riparian zone is defined as the area of land adjoining a river channel, including the river bank but not the wider floodplain.

It can provide shade to cool the stream, stabilise stream banks, and act as a source of nutrients and woody debris (provided by SKM Enviros).

2. Site selection and design - targeting planting and fencing

2.1 Factors influencing water temperature Figure 2 indicates the complex interplay of some of the dominant factors influencing river water temperature and shows how the efficacy of riparian shading in cooling stream temperatures reduces downstream.

Planting the banks of the headwater streams is likely to offer the greatest benefits to water temperature within a river basin12. The graph also indicates the impact that tributary inflows can have on stream temperature and may indicate that all tributaries to a point should be considered for tree planting to maximise the benefits. These upstream/ downstream influences obviously depend on the size of catchments and channels and no evidence has yet come to light about how to quantify how far such impacts extend downstream in UK catchments.

The focus of riparian planting or fencing to reduce instream temperatures should be in uplands or head waters on smaller low order streams (see Error! Reference source not found.). Stream orientation hould also be considered in the design of tree planting or fencing schemes to optimise shading over the stream channel. In addition to the creation of riparian shade in the streams of the upper catchment, there may be benefits of planting riparian trees further downstream to create thermal refuges for fish.

Specific local issues will influence site selection for tree planting or fencing. An important consideration will be the availability of land and support of landowners. Other catchment objectives such as the reduction of flood risk and the impacts of diffuse pollution13 will influence choice of species, planting design and site selection.

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